Method for detecting optical wavelength

ABSTRACT

An optical wavelength detecting device, the device including: a polarizer configured to transform an incident light into a polarized light; a detecting element configured to receive the polarized light and form a temperature difference or a potential difference between two points of the detecting element, wherein the detecting element includes a carbon nanotube structure including a plurality of carbon nanotubes oriented along the same direction, and angles between a polarizing direction of the polarized light and an oriented direction of the plurality of carbon nanotubes is adjustable; a measuring device electrically connected to the detecting element and configured to measure the temperature difference or the potential difference; a data processor electrically connected to the measuring device and configured to obtain the optical wavelength by calculating and analyzing the temperature difference or the potential difference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. § 119 from China Patent Application No. 201610042563.6, filed on Jan. 22, 2016, in the China Intellectual Property Office, the disclosure of which is incorporated herein by reference.

FIELD

The subject matter herein generally relates to a method for detecting optical wavelength.

BACKGROUND

It has always been an interesting topic for people to explore usages of specific wavelengths of light. For example, the light can show different colors because of different wavelengths of light, and the light can be directly used as indicator tools in our life. Certainly, the light having specific wavelength can be applied to many fields. But in the study of the specific wavelength of light application, it is necessary to be able to measure the wavelength simply and accurately.

Currently, there are some methods of measuring the specific wavelength, such as measurement using light interference, or measurement using light diffraction. But these methods are carried out manually and complicated, and workers who carry out these methods must have high levels. Also, measurement errors of these methods are large, and the measurement scale is limited. The detection equipment related to these methods are very big and complicated.

What is needed, therefore, is to provide a method for detecting optical wavelength for solving the problem discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with references to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. Implementations of the present technology will now be described, by way of example only, with reference to the attached figures, wherein:

FIG. 1 is a schematic view of one embodiment of a device for detecting optical wavelength.

FIG. 2 is a structural schematic view of a drawn carbon nanotube film used in the device of FIG. 1.

FIG. 3 shows a Scanning Electron Microscope (SEM) image of the drawn carbon nanotube film used in the device of FIG. 1.

FIG. 4 is a SEM image of a non-twisted carbon nanotube wire used in the device of FIG. 1.

FIG. 5 is a SEM image of a twisted carbon nanotube wire used in the device of FIG. 1.

FIG. 6 is a diagram showing a relationship between a light transmittance of a carbon nanotube structure in the device of FIG. 1 and an optical wavelength.

FIG. 7 is a schematic view of one embodiment of a device for detecting optical wavelength.

FIG. 8 is a schematic view of stacked arrangements of semiconductor carbon nanotube layers.

FIG. 9 is a flow chart of a method for using the device for detecting optical wavelength.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. The drawings are not necessarily to scale, and the proportions of certain parts may be exaggerated to better illustrate details and features. The description is not to be considered as limiting the scope of the embodiments described herein.

Several definitions that apply throughout this disclosure will now be presented.

The connection can be such that the objects are permanently connected or releasably connected. The term “substantially” is defined to be essentially conforming to the particular dimension, shape or other word that substantially modifies, such that the component need not be exact. The term “comprising” means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in a so-described combination, group, series and the like. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one.

Referring to FIG. 1, an embodiment of an optical wavelength detecting device 100 comprises a polarizer 101, a detecting element 102, a first electrode 103, a second electrode 104, a measuring device 105 and a data processor 108. The polarizer 101 is spaced from the detecting element 102 and used for generating polarized light. The first electrode 103 and the second electrode 104 are spaced apart from each other and electrically connected to the detecting element 102. The detecting element 102 is electrically connected to the measuring device 105 by the first electrode 103 and the second electrode 104. The detecting element 102 comprises a carbon nanotube structure. The carbon nanotube structure comprises a plurality of carbon nanotubes oriented along the same direction and is in direct contact with the first electrode 103 and the second electrode 104. The measuring device 105 is electrically connected to the first electrode 103 and the second electrode 104. The data processor 108 is connected to the measuring device 105.

The polarizer 101 and the detecting element 102 are parallel and spaced from each other. The polarized light emitting from the polarizer 101 can irradiate the carbon nanotube structure of the detecting element 102. An oriented direction of the carbon nanotubes of the carbon nanotube structure can be the same as a direction from the first electrode 103 to the second electrode 104. The measuring device 105 is used to measure a temperature difference or potential difference of the carbon nanotube structure. A light transmittance can be obtained by calculating the difference of temperature or potential, and the optical wavelength can be obtained by reading the light transmittance.

The polarizer 101 is used for transforming light into polarized light. The polarizer 101 can be any kinds of materials that can transform light into polarized light. The polarizer 101 can be yttrium aluminate, iodine, calcite or any other suitable material. The polarizer 101 can be a rotatable structure to form any angles between a polarized light direction and the oriented direction of the carbon nanotubes. The polarizer 101 can be rotated in a plane of the polarizer 101 to alter the angles between the direction of the polarized light and the oriented direction of the carbon nanotubes. Thus the angles between the polarized light direction and the oriented direction of the carbon nanotubes can be at any value in 0-90 degree. The polarizer 101 can be rotated by a rotating bracket. The polarized light can further irradiate a part of the carbon nanotube structure surface to generate a temperature or potential difference in the carbon nanotube structure. A first point in the part surface which is irradiated is selected. A second point in the part surface which is not irradiated is selected. The temperature or potential difference between the first point and the second point increase as the distance between the first point and the second point increases. In one embodiment, the carbon nanotube structure is strap-shaped, and the first point and the second point are two opposite ends of the carbon nanotube structure.

The detecting element 102 comprises the carbon nanotube structure. The carbon nanotube structure comprises a plurality of carbon nanotubes oriented along the same direction. The oriented direction of carbon nanotubes is parallel with a carbon nanotube structure surface. In one embodiment, the detecting element 102 is a carbon nanotube layer, and the carbon nanotube layer consists of a plurality of carbon nanotubes, joined to each other end to end by van der Waals attractive force. The carbon nanotubes in the carbon nanotube structure can be single-walled, double-walled, or multi-walled carbon nanotubes. A diameter of each single-walled carbon nanotube ranges from about 0.5 nanometers (nm) to about 10 nm. A diameter of each double-walled carbon nanotube ranges from about 1 nm to about 15 nm. A diameter of each multi-walled carbon nanotube ranges from about 1.5 nm to about 50 nm. The carbon nanotubes can be N-type carbon nanotubes or P-type carbon nanotubes.

The carbon nanotube structure can be a free-standing structure. The free-standing structure is that the carbon nanotube structure can keep a certain shape without any supporter, which is different from powder or liquid. The carbon nanotube structure comprises a plurality of carbon nanotubes joined to each other by van der Waals attractive force, thereby forming a certain shape. When the carbon nanotube structure is a free-standing structure, the detecting element 102 can be suspended. The carbon nanotube structure comprises at least one carbon nanotube film, at least one carbon nanotube wire structure, or a combination thereof. The carbon nanotube structure is a layer structure of a plurality of parallel arrangement carbon nanotubes.

Carbon Nanotube Film

In one embodiment, the carbon nanotube film comprises at least one carbon nanotube segment. Referring to FIG. 2, each carbon nanotube segment 143 comprises a plurality of carbon nanotubes 145 approximately parallel to each other, and combined by van der Waals attractive force. The carbon nanotube segments 143 can vary in width, thickness, uniformity, and shape. The carbon nanotubes 145 in the carbon nanotube segments 143 are also oriented along a preferred orientation.

Carbon Nanotube Film Manufactured by Method 1

In one embodiment, the carbon nanotube film can be drawn from a carbon nanotube array, to form a drawn carbon nanotube film. In the present embodiment, the drawn carbon nanotube film can be pulled out from a super-aligned carbon nanotube array on a substrate. The drawn carbon nanotube film comprises a plurality of successive and oriented carbon nanotubes 145 joined end to end by van der Waals attractive force. Referring to FIG. 3, each drawn carbon nanotube film comprises a plurality of successively oriented carbon nanotube segments 143 joined end-to-end by van der Waals attractive force. The thickness of the drawn carbon nanotube film is in a range from about 0.5 nm to about 100 micrometers (μm). Examples of a drawn carbon nanotube film are taught by U.S. Pat. No. 7,045,108 to Jiang et al., and WO 2007015710 to Zhang et al.

Carbon Nanotube Film Manufactured by Method 2

In another embodiment, the carbon nanotube film comprises one carbon nanotube segment 143. Referring to FIG. 3, the carbon nanotube segment 143 comprises a plurality of carbon nanotubes 145 substantially arranged along the same direction. The carbon nanotubes 145 in the carbon nanotube film are substantially parallel to each other and have almost equal lengths, and are combined side by side via van der Waals attractive force. The width of the carbon nanotube film is equal to the length of the carbon nanotubes 145, thus at least one carbon nanotube 145 spans the entire width of the carbon nanotube film. The carbon nanotube film can be produced by growing a strip-shaped carbon nanotube array, and pushing the strip-shaped carbon nanotube array down along a direction substantially perpendicular to a length of the strip-shaped carbon nanotube array, and has a length of about 20 μm to about 10 millimeters (mm). The length of the carbon nanotube film is only limited by the length of the strip. A larger carbon nanotube film also can be formed by having a plurality of the strips lined up side by side and folding the carbon nanotubes 145 grown thereon over such that there is overlap between the carbon nanotubes 145 on adjacent strips.

Carbon Nanotube Film Manufactured by Method 3

In some embodiments, the carbon nanotube film comprising one carbon nanotube segment 143 can also be produced by a method adopting a “kite-mechanism.” The carbon nanotube film can have carbon nanotubes 145 with a length greater than 10 centimeters (cm). The carbon nanotube film can be produced by providing a growing substrate with a catalyst layer located thereon, placing the growing substrate adjacent to the insulating substrate in a chamber, heating the chamber to a growth temperature for carbon nanotubes 145 under a protective gas, introducing a carbon source gas along a gas flow direction, and growing a plurality of carbon nanotubes 145 on the insulating substrate. After introducing the carbon source gas into the chamber, the carbon nanotubes 145 will start to grow under the effect of the catalyst. One end (e.g., the root) of the carbon nanotubes 145 is kept unchanged on the growing substrate, and the other end (e.g., the top/free end) of the carbon nanotubes 145 will grow continuously. The growing substrate is near an inlet of the introduced carbon source gas, such that the carbon nanotubes 145 floats above the insulating substrate with the roots of the carbon nanotubes 145 still attached on the growing substrate, as the carbon source gas is continuously introduced into the chamber. The length of the carbon nanotubes 145 depends on the growth conditions. After growth has been stopped, the carbon nanotubes 145 are located entirely on the insulating substrate. The carbon nanotubes 145 roots are then separated from the growing substrate. This can be repeated many times to obtain many layers of carbon nanotube films on a single insulating substrate. The adjacent carbon nanotubes 145 can be adhered together by van der Waals attractive force and being substantially parallel to each other, with a distance of adjacent carbon nanotubes 145 being less than 5 μm.

The carbon nanotube structure can comprise at least two stacked and/or coplanar carbon nanotube films. These coplanar carbon nanotube films can also be stacked one upon other films. The carbon nanotubes 145 in two adjacent carbon nanotube films are substantially parallel. Adjacent carbon nanotube films can be combined only by the van der Waals attractive force. The number of layers of the carbon nanotube films is not limited so that a carbon nanotube structure can have different widths and areas. Stacking the carbon nanotube films will add to the structural strength of the carbon nanotube structure.

Carbon Nanotube Wire Structure

In other embodiments, the carbon nanotube structure comprises one or more carbon nanotube wire structures. The carbon nanotube wire structure comprises carbon nanotube cables that comprise of twisted carbon nanotube wires, untwisted carbon nanotube wires, or combinations thereof. The carbon nanotube cable comprises two or more carbon nanotube wires, twisted or untwisted that are twisted or bundled together. The carbon nanotube wires in the carbon nanotube wire structure can be substantially parallel to each other to form a bundle-like structure or twisted with each other to form a twisted structure. When the carbon nanotube structure comprises a plurality of carbon nanotube wire structures, the carbon nanotube wire structures can be coplanar and substantially parallel to each other, or stacked and substantially parallel to each other. Referring to FIG. 4, when the carbon nanotube structure comprises one carbon nanotube wire structure, the carbon nanotube wire structure bends orderly in a surface, thereby forming a planar structure, and the carbon nanotube wires of the carbon nanotube wire structure are substantially parallel to and connect to each other and arranged.

The non-twisted carbon nanotube wire can be formed by treating the drawn carbon nanotube film with an organic solvent. The drawn carbon nanotube film is treated by applying the organic solvent to the drawn carbon nanotube film to soak the entire surface of the drawn carbon nanotube film. After being soaked by the organic solvent, the adjacent parallel carbon nanotubes in the drawn carbon nanotube film will bundle together, due to the surface tension of the volatile organic solvent as the organic solvent volatilizes, and thus, the drawn carbon nanotube film will be shrunk into a non-twisted carbon nanotube wire. Referring to FIG. 4, the non-twisted carbon nanotube wire comprises a plurality of carbon nanotubes substantially oriented along the same direction (e.g., a direction along the length of the non-twisted carbon nanotube wire). The carbon nanotubes are substantially parallel to the axis of the non-twisted carbon nanotube wire. The non-twisted carbon nanotube wire comprises a plurality of carbon nanotube segments joined end-to-end by van der Waals attractive force. Each carbon nanotube segment comprises a plurality of carbon nanotubes substantially parallel to each other and combined by van der Waals attractive force. A length of the non-twisted carbon nanotube wire can be arbitrarily set as desired. A diameter of the non-twisted carbon nanotube wire can range from about 0.5 nm to about 100 μm. In one embodiment, the diameter of the non-twisted carbon nanotube wire is about 50 μm. Examples of the non-twisted carbon nanotube wire are taught by US Patent Application Publication US 2007/0166223 to Jiang et al.

The twisted carbon nanotube wire can be formed by twisting a drawn carbon nanotube film by using a mechanical force to turn the two ends of the drawn carbon nanotube film in opposite directions. Referring to FIG. 5, the twisted carbon nanotube wire comprises a plurality of carbon nanotubes oriented along an axial direction of the twisted carbon nanotube wire. The carbon nanotubes are aligned in a helix around the axis of the carbon nanotube twisted wire. More specifically, the twisted carbon nanotube wire comprises a plurality of successive carbon nanotube segments joined end-to-end by van der Waals attractive force. Each carbon nanotube segment comprises a plurality of carbon nanotubes substantially parallel to each other and combined by van der Waals attractive force. The carbon nanotube segment has arbitrary length, thickness, uniformity, and shape. A length of the carbon nanotube wire can be arbitrarily set as desired. A diameter of the twisted carbon nanotube wire can range from about 0.5 nm to about 100 μm. Further, the twisted carbon nanotube wire can be treated with a volatile organic solvent, before or after being twisted. After being soaked by the organic solvent, the adjacent parallel carbon nanotubes in the twisted carbon nanotube wire will bundle together, due to the surface tension of the organic solvent as the organic solvent volatilizes. The specific surface area of the twisted carbon nanotube wire will decrease, but the density and strength of the twisted carbon nanotube wire will increase. It is understood that the twisted and non-twisted carbon nanotube cables can be produced by methods that are similar to the methods of making twisted and non-twisted carbon nanotube wires.

In one embodiment, the carbon nanotube structure is composed of at least one carbon nanotube film and at least one carbon nanotube wire structure. The carbon nanotubes in the carbon nanotube film are substantially parallel to the carbon nanotube wire structures.

The thickness of the carbon nanotube structure can be selected as desired. The carbon nanotube structure is thick enough to guarantee that the detecting element 102 can detect the wavelength and the measured error is small. In one embodiment, the thickness of the carbon nanotube structure can range from about 0.5 nm to about 5 μm. The thickness of the carbon nanotube structure cannot be too thick (greater than 5 μm). If the thickness of the carbon nanotube structure is greater than 5 μm, because the incident light cannot pass through the carbon nanotube structure, a part of the carbon nanotubes cannot be irradiated by the light. The optical wavelength detecting device 100 has a large measurement error.

Referring to FIG. 6, in the carbon nanotube structure, the carbon nanotubes are substantially parallel and extend along the same direction, the polarized light is selectively absorbed by the carbon nanotube structure according to the polarized light direction and polarized light wavelength. As an angle between the polarized light direction and the carbon nanotubes is unchanged, the polarized light transmittance increases monotonously as the wavelength increases. When the polarized light wavelength is kept unchanged, the angle changes can make the polarized light transmittance being changed. When the polarizing direction is substantially parallel to the carbon nanotubes orientation, the polarized light is easily absorbed by the carbon nanotube structure, so the polarized light transmittance is very low. When the polarizing direction is substantially perpendicular to the carbon nanotubes orientation, the polarized light can pass through the carbon nanotube structure easily, so the polarized light transmittance is very high. Due to the polarized light absorbed by the carbon nanotube structure can be converted into heat energy, the heat energy can produce temperature difference in the carbon nanotube structure and the temperature difference can change into the potential difference. The carbon nanotube structure can measure the polarized light wavelength as the temperature and voltage changes.

In one embodiment, the detecting element 102 can further comprise an insulating substrate 106 for supporting the carbon nanotube structure. The carbon nanotube structure is located on an insulating substrate 106 surface. The insulating substrate 106 material can be rigid materials (e.g., p-type or n-type silicon, silicon with a silicon dioxide layer formed thereon, crystal, crystal with an oxide layer formed thereon), or flexible materials (e.g., plastic or resin). The insulating substrate 106 material can be polyethylene terephthalate, polyethylene naphthalate two formic acid glycol ester (PEN), or polyimide. In one embodiment, the detecting element 102 comprises an insulating substrate 106, and the insulating substrate 106 material is polyethylene terephthalate.

In one embodiment, the detecting element 102 can be rotated freely in the detecting element plane to form different angles between the polarized light direction and the carbon nanotubes orientation. The polarizer 101 can also be rotated freely in the polarizer 101 plane to adjust the angles between the polarized light direction and the carbon nanotubes orientation.

The first electrode 103 and the second electrode 104 are made of conductive material. The first electrode 103 or the second electrode 104 shape is not limited and can be lamellar, rod, wire, block, or other shapes. A first and second electrodes 103, 104 material can be one metal or more metals, conductive adhesive, carbon nanotube, indium tin oxide, or other material. In one embodiment, the first electrode 103 and the second electrode 104 are rod-shaped metal electrodes. The carbon nanotubes in the carbon nanotube structure extend along a direction from the first electrode 103 to the second electrode 104. Some carbon nanotube structures have large specific surface area and better adhesion ability under the effect of the van der Waals attractive force and can be adhered directly to the first electrode 103 and the second electrode 104. This will result in good electrical contact between the carbon nanotube structure and the first and second electrodes 103, 104. Furthermore, a conductive adhesive layer (not shown) can be further provided between the first electrode 103 and/or the second electrode 104 and the carbon nanotube structure. The conductive adhesive layer can be applied to the carbon nanotube structure surface to provide electrical contact and better adhesion between the first and second electrodes 103, 104 and the carbon nanotube structure.

The measuring device 105 can be a voltage measuring device to measure the carbon nanotube structure voltage differences or a thermocouple device to measure the temperature differences of the carbon nanotube structure. The measuring device 105 can be electrically connected to the carbon nanotube structure by the first electrode 103 and the second electrode 104, thus a circuit is formed. When the carbon nanotube structure generates a potential between the first electrode 103 and the second electrode 104 because of the temperature difference, the carbon nanotube structure is equivalent to a power, and a current is generated in the circuit. The measuring device 105 can measure the carbon nanotube structure potential directly without any other power supply device. When the measuring device 105 is the thermocouple device, the thermocouple device can measure the temperature difference between the opposite two ends of the carbon nanotube structure. A measuring position can be selected as desired. When the polarized light irradiates a first part surface of the carbon nanotube structure, a first point in the first part surface which is irradiated is selected, a second point in a second part surface which is not irradiated is selected, the measuring device 105 measures the temperature difference or the potential difference between the first point and the second point. The carbon nanotube structure can further comprise a P-type semiconductor carbon nanotube layer and an N-type semiconductor carbon nanotube layer in contact with each other to form a P-N junction. A third point in the P-type semiconductor carbon nanotube layer is selected, a fourth point in the N-type semiconductor carbon nanotube layer is selected. The measuring device 105 can only measure the potential difference between the third point and the fourth point when the polarized light irradiates the P-N junction.

The data processor 108 is used to obtain the optical wavelength by calculating and analyzing the temperature difference or the potential difference. The data processor 108 comprise a database of transmittance-angle-wavelength values and can calculate the temperature difference or the potential difference to obtain the polarized light transmittance. Then the optical wavelength can be obtained according to the values of transmittance in the database of transmittance-angle-wavelength values.

The principle of measuring the optical wavelength by using the optical wavelength detecting device 100 can be further described in detail. Firstly, a beam of incident light is provided, and the incident light power is determined. The power is set to P, and the optical wavelength is set to λ. Secondly, the polarized light is formed by using the polarizer 101 to polarize the incident light. There is an amount of energy loss during the incident light passing through the polarizer 101. A transmittance of the polarizer is set to α. Referring to FIG. 6, as the angle between the polarized light direction and the carbon nanotubes changes, the polarized light transmittances are different. The transmittance is set to T. When the polarizing direction is substantially parallel to the carbon nanotubes orientation, the transmittance is set to T_(λII). When the polarizing direction is substantially perpendicular to the carbon nanotubes orientation, the transmittance is set to T_(λ□). When the polarized light irradiates the carbon nanotube structure, an electric potential is produced by the temperature difference induced in the carbon nanotube structure. An energy conversion efficiency is set to β. The energy conversion efficiency β is only related to devices comprising carbon nanotubes and is not related to the carbon nanotubes orientation.

So a potential difference U of both carbon nanotube structure ends is defined by a formula (1), U=√{square root over (PRαβ(1−T))}  (1)

-   -   R is a carbon nanotube structure resistance. The carbon nanotube         structure resistance is approximately unchanged despite the         temperature variation range is not large. At the same time, a         carbon nanotube structure has been determined, the resistance is         kept unchanged and isn't related to the polarization direction         of light and wavelength.

The polarizing direction is substantially parallel to the carbon nanotubes orientation, the potential difference of the carbon nanotube structure is U_(II), U _(II)=√{square root over (PRαβ(1−T_(λII)))}.

The polarizing direction is substantially perpendicular to the carbon nanotubes orientation, the potential difference of the carbon nanotube structure is U_(⊥), U _(⊥)=√{square root over (PRαβ(1−T _(λ⊥)))}

-   -   K is defined,

$\mspace{20mu}{{K = \frac{U_{\coprod}}{U_{\bot}}},{K = {\frac{U_{\coprod}}{U_{\bot}} = {\sqrt{\frac{1 - T_{\lambda\coprod}}{1 - T_{\lambda\bot}}} = {\sqrt{\frac{1 - T_{\lambda\bot} + T_{\lambda\bot} - T_{\lambda\coprod}}{1 - T_{\lambda\bot}}} = \sqrt{1 + \frac{T_{\lambda\bot} - T_{\lambda\coprod}}{1 - T_{\lambda\bot}}}}}}}}$

When the angle between the carbon nanotubes orientation and polarizing direction is unchanged, a transmittance difference between arbitrary wavelength is approximately kept unchanged. T _(λ⊥) −T _(λII) =C, the C is unchanged.

$\begin{matrix} {K = {\sqrt{1 + \frac{T_{\lambda\;\bot} - T_{\lambda\coprod}}{1 - T_{\lambda\bot}}} = \sqrt{1 + \frac{C}{1 - T_{\lambda\bot}}}}} & (2) \end{matrix}$

Referring to the formula (2), the values of K and T_(λ⊥) are monotonic. When the angle between the carbon nanotubes orientation and polarizing direction is unchanged, the value of T_(λ⊥) increases as the wavelength increases. So the values of K and wavelength of incident light are monotonic.

A formula (3) can be obtained by changing the formula (2),

$\begin{matrix} {T_{\lambda\bot} = {1 - \frac{C}{K^{2} - 1}}} & (3) \end{matrix}$

Referring to the formula (3), T_(λ⊥) can be obtained by calculating the value of K. The value of K can be obtained by calculating the values of U_(II) and U_(□) of the carbon nanotube structure under different conditions. When the angle between the carbon nanotubes orientation and polarizing direction is unchanged, the polarized light transmittance corresponds to a unique wavelength value. The optical wavelength can be obtained according to the values of transmittance in the database of transmittance-angle-wavelength values of the data processor 108. According to the Seebeck effect, U=ρ ΔT, ρ is the Seebeck coefficient and related to materials. The temperature differences change as the voltage value changes, and the wavelength value of incident light can also be calculated by the temperature differences.

Referring to FIG. 7, one embodiment of an optical wavelength detecting device 200 comprises a polarizer 201, a detecting element 202, a first electrode 203, a second electrode 204, and a measuring device 205, and a data processor 208. The polarizer 201 is spaced from the detecting element 202 and used for generating polarized light. The first electrode 203 and the second electrode 204 are spaced apart from each other. The detecting element 202 is electrically connected to the measuring device 205 by the first electrode 203 and the second electrode 204. The detecting element 202 comprises a carbon nanotube structure. The carbon nanotube structure comprises a plurality of carbon nanotubes oriented along the same direction, and is electrically connected to the first electrode 203 and the second electrode 204. The measuring device 205 is electrically connected to the first electrode 203 and the second electrode 204. The data processor 208 is connected to the measuring device 205.

The device 200 is similar to the device 100 except the detecting element 202 comprises a P-N junction composed of a P-type semiconductor carbon nanotube layer 2021 and an N-type semiconductor carbon nanotube layer 2022. The P-type semiconductor carbon nanotube layer 2021 and the N-type semiconductor carbon nanotube layer 2022 can be stacked with each other or arranged side by side in the same plane. When the P-type semiconductor carbon nanotube layer 2021 and the N-type semiconductor carbon nanotube layer 2022 are arranged side by side in the same plane, the oriented direction of carbon nanotubes in the P-type semiconductor carbon nanotube layer 2021 is the same as the oriented direction of carbon nanotubes in the N-type semiconductor carbon nanotube layer 2022. And a contact surface of the P-type semiconductor carbon nanotube layer 2021 and the N-type semiconductor carbon nanotube layer 2022 is perpendicular to the oriented direction of carbon nanotubes. When the P-type semiconductor carbon nanotube layer 2021 and the N-type semiconductor carbon nanotube layer 2022 are stacked with each other, the contact surface of the P-type semiconductor carbon nanotube layer 2021 and the N-type semiconductor carbon nanotube layer 2022 is parallel to the oriented direction of carbon nanotubes. Referring to FIG. 8, the stacked arrangement can also be sandwich structure, such as P-N-P or N-P-N. It is necessary to satisfy that the P-type semiconductor carbon nanotube layer 2021 and the N-type semiconductor carbon nanotube layer 2022 are electrically connected to the first electrode 203 and the second electrode 204. When the N-type semiconductor carbon nanotube layer is sandwiched between a first P-type semiconductor carbon nanotube layer and a second P-type semiconductor carbon nanotube layer, a first part of the N-type semiconductor carbon nanotube layer extends to the outside of the two P-type semiconductor carbon nanotube layers to form an exposed part, and the exposed part of the N-type semiconductor carbon nanotube layer is coated by the second electrode 204. Additionally, the first electrode 203 comprises a first electrode unit and a second electrode unit, the first electrode unit is located on a second part of the first P-type semiconductor carbon nanotube layer, the second electrode unit is located on a third part of the second P-type semiconductor carbon nanotube layer. And the first electrode unit and the second electrode unit are electrically connected with each other. When the P-type semiconductor carbon nanotube layer is sandwiched between a first N-type semiconductor carbon nanotube layer and a second N-type semiconductor carbon nanotube layer, a first part of the P-type semiconductor carbon nanotube layer extends to the outside of the two N-type semiconductor carbon nanotube layers to form an exposed part, and the exposed part of the P-type semiconductor carbon nanotube layer is coated by the second electrode 204. And the first electrode 203 comprises a first electrode unit and a second electrode unit, the first electrode unit is located on a second part of the first N-type semiconductor carbon nanotube layer, the second electrode unit is located on a third part of the second N-type semiconductor carbon nanotube layer. And the first electrode unit and the second electrode unit are electrically connected with each other. In one embodiment, the P-type semiconductor carbon nanotube layer 2021 and the N-type semiconductor carbon nanotube layer 2022 are arranged side by side in the same plane.

When the carbon nanotube structure containing P-N junction is irradiated by the incident light, the incident light energy is directly converted into electrical energy and is not converted into heat energy. The temperature difference between a portion of the carbon nanotube structure irradiated with the incident light and a non-irradiated portion is small and negligible. In one embodiment, the effect of incident light on carbon nanotubes is changed from thermoelectric effect to photoelectric effect, which reduced the loss of intermediate energy. The structure with P-N junction enhances the sensitivity of the carbon nanotube structure to the incident light, thus the measurement of the device is more accurate.

The device 100 for detecting optical wavelength has following advantages. Due to the device 100 comprises the polarizer and the carbon nanotube structure composed of a plurality of carbon nanotubes, the optical wavelength can be measured by adjusting angles between the polarizing direction of polarized light and the carbon nanotubes orientation. The method of measuring the optical wavelength is simple. The carbon nanotube structure can also play the role of power, so an additional power supply is not required in the device 100. The device 100 structure is simple. The effect of incident light on carbon nanotubes can be changed from thermoelectric effect to photoelectric effect, thus the loss of intermediate energy is reduced. The carbon nanotube structure with P-N junction enhances the sensitivity of the carbon nanotube structure to the incident light, thus the device measurement is more accurate.

Referring to FIG. 9, a method of using the optical wavelength detecting device 100 comprises:

S1, irradiating a polarizer by using a light, wherein the light is polarized into a polarized light;

S2, the polarized light passing through the carbon nanotube structure, the angle between the polarizing direction of polarized light and the carbon nanotubes orientation being θ₁, the potential difference and the temperature difference of the carbon nanotube structure being U₁, Δt₁;

S3, rotating the polarizer, making the angle between the polarizing direction of polarized light and the carbon nanotubes orientation being θ₂, the potential difference and the temperature difference of the carbon nanotube structure being U₂, Δt₂;

S4, obtaining the transmittance T_(λ1) and T_(λ2) by calculating the potential differences and the temperature differences using the formula

$\frac{U_{1}}{U_{2}} = {\frac{\Delta\; t_{1}}{\Delta\; t_{2}} = \sqrt{1 + \frac{C}{1 - T_{\lambda\; 2}}}}$ or ${\frac{U_{2}}{U_{1}} = {\frac{\Delta\; t_{2}}{\Delta\; t_{1}} = \sqrt{1 - \frac{C}{1 - T_{\lambda\; 1}}}}},{C = {T_{\lambda\; 2} - T_{\lambda\; 1}}},$ the C is unchanged;

S5, obtaining the optical wavelength by analyzing the transmittance with a database of transmittance-angle-wavelength values.

In step S2, the potential difference or the temperature difference can be produced in the carbon nanotube structure after being irradiated by the light polarized by the polarizer. The temperature difference can be generated in the carbon nanotube structure, and the temperature difference can be converted into the potential difference. The potential difference or the temperature difference increases as the distance between the irradiated portion and the non-irradiated portion of the carbon nanotube structure increases. When the carbon nanotube structure comprises an N-type semiconductor carbon nanotube layer and a P-type semiconductor carbon nanotube layer, the potential difference can be directly generated between the N-type semiconductor carbon nanotube layer and the P-type semiconductor carbon nanotube layer.

In step S4, when the angle between the carbon nanotubes orientation and the polarizing direction of polarized light is unchanged, the polarized light transmittance corresponds to a unique wavelength value.

The embodiments shown and described above are only examples. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, including in matters of shape, size, and arrangement of the parts within the principles of the present disclosure up to, and including, the full extent established by the broad general meaning of the terms used in the claims.

Depending on the embodiment, certain of the steps of methods described may be removed, others may be added, and the sequence of steps may be altered. The description and the claims drawn to a method may comprise some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps. 

What is claimed is:
 1. A method of detecting wavelength of a light, the method comprising: irradiating a polarizer by light, wherein the light is polarized into a polarized light; allowing the polarized light to pass through a carbon nanotube structure comprising a plurality of carbon nanotubes oriented along the same direction, wherein a first angle between a polarizing direction of the polarized light and an orientation of the plurality of carbon nanotubes is defined as θ₁, and a first potential difference is generated between two points of the carbon nanotube structure and defined as U₁; making a second angle between the polarizing direction of the polarized light and the orientation of the plurality of carbon nanotubes being defined as θ₂, and a second potential difference between the two points of the carbon nanotube structure being defined as U_(2;) obtaining transmittances T_(λ1) and T_(λ2) by calculating the first potential difference and the second potential difference using a formula ${\frac{U_{1}}{U_{2}} = \sqrt{1 + \frac{C}{1 - T_{\lambda\; 2}}}},{\frac{U_{2}}{U_{1}} = \sqrt{1 - \frac{C}{1 - T_{\lambda\; 1}}}},{{{and}\mspace{14mu} C} = {T_{\lambda\; 2} - T_{\lambda\; 1}}},$  wherein the C is unchanged; obtaining a wavelength of the light from a database of transmittance -angle-wavelength values according to the transmittances T_(λ1) and T_(λ2).
 2. The method as claimed in claim 1, wherein the polarized light irradiates a first part of the carbon nanotube structure, a first point in the first part of the carbon nanotube structure which is irradiated is selected, a second point in a second part of the carbon nanotube structure which is not irradiated is selected, and the potential difference between the first point and the second point is measured.
 3. The method as claimed in claim 1, wherein the carbon nanotube structure comprises a P-type semiconductor carbon nanotube layer and an N-type semiconductor carbon nanotube layer in contact with each other to form a P-N junction, a third point in the P-type semiconductor carbon nanotube layer is selected, a fourth point in the N-type semiconductor carbon nanotube layer is selected, and the potential difference between the third point and the fourth point is measured.
 4. The method as claimed in claim 1, wherein the angle is changed by rotating the polarizer.
 5. The method as claimed in claim 4, wherein the polarizer is rotated by a rotating bracket.
 6. The method as claimed in claim 1, wherein the transmittance of the polarized light corresponds to an unique wavelength value when the angle between the orientation of the plurality of carbon nanotubes and the polarizing direction is unchanged.
 7. The method as claimed in claim 1, wherein the potential difference is measured by a voltage measuring device.
 8. A method of detecting wavelength of a light, the method comprising: irradiating a polarizer by the light, wherein the light is polarized into a polarized light; allowing the polarized light to irradiate a carbon nanotube structure comprising a plurality of carbon nanotubes oriented along the same direction, wherein a first angle between a polarizing direction of the polarized light and an orientation of the plurality of carbon nanotubes is defined as θ₁, and a first temperature difference is generated between two points of the carbon nanotube structure and defined as Δt₁; making a second angle between the polarizing direction of the polarized light and the orientation of the plurality of carbon nanotubes being defined as θ₂, and a second temperature difference is generated between the two points of the carbon nanotube structure and is defined as Δt₂; obtaining transmittances T_(λ1) and T_(λ2) by calculating the first temperature difference and the second temperature difference using a formula ${\frac{\Delta\; t_{1}}{\Delta\; t_{2}} = \sqrt{1 + \frac{C}{1 - T_{\lambda\; 2}}}},{\frac{\Delta\; t_{2}}{\Delta\; t_{1}} = \sqrt{1 - \frac{C}{1 - T_{\lambda\; 1}}}},{{{and}\mspace{14mu} C} = {T_{\lambda\; 2} - T_{\lambda\; 1}}},$  wherein the C is unchanged; obtaining a wavelength of the light from a database of transmittance -angle-wavelength values according to the transmittances T_(λ1) and T_(λ2).
 9. The method as claimed in claim 8, wherein the potential difference U₁=ρΔt₁, the potential difference U₂=ρΔt₂, ρ is a Seebeck coefficient.
 10. The method as claimed in claim 8, wherein the allowing the polarized light to irradiate the carbon nanotube structure comprises: dividing the carbon nanotube structure to a first part comprising a first point and a second part comprising a second point; allowing the polarized light only to irradiate the first part; the first or second temperature differences being generated between the two points of the carbon nanotube structure comprises generating the first or second temperature differences between the first point and the second point.
 11. The method as claimed in claim 8, wherein the temperature differences is measured by a thermocouple device. 